Recently, production of bio-based fuels has become imperative due to the rapid increase in the prices of petroleum and serious environmental pollution. Biodiesel, one of the bio-based fuels, is produced by transesterification of a triglyceride from vegetable oils or animal fats.
Mass production of biodiesel has resulted in large-scale production of glycerol as a by-product with about 7.7 billion pounds of glycerol produced per 1 billion gallons of biodiesel. The production of glycerol has increased very rapidly and is estimated at about 3.2 billion pounds per year in the United States and 8 billion pounds per year worldwide. As a consequence, the price of glycerol has decreased almost ten-fold over the past 2 years. The market price of crude glycerol was 5 to 15 cents/lb in 2004, but is now reportedly less than 2.5 cents/lb. In comparison, the price of glucose is currently about 5 cents/lb and is increasing gradually. Should the current trend continue, the continuous decrease in the price of glycerol might be considered inevitable.
A microorganism may use glycerol as a carbon source and generate various fermentation products using the glycerol. 3-Hydroxypropionic acid (“3-HP”; C3H6O3—MW 90.08) is a compound applicable to various chemical processes, which may be produced from a renewable resource such as glycerol. 3-HP may be produced by both chemical synthetic methods and biological methods.
The chemical methods to produce 3-HP may include (1) a method of producing 3-HP by using palladium as a catalyst from 1,3-propanediol as a starting material, (2) a method of producing 3-HP in presence of palladium and platinum as catalysts from 3-hydroxypropionaldehyde, and (3) a method of producing 3-HP (e.g., with a selectivity of 91% and a yield of 34%) by reaction of an acrylic acid as a starting material with an ion exchange resin (Amberlyst™ 15) as a solid acid catalyst at 100° C. for 40 hours in a high-pressure reaction vessel.
However, most of these chemicals are toxic and carcinogenic. In addition, the chemicals consume a large quantity of energy under high temperature and pressure and exhaust a large quantity of pollutants.
Biological 3-HP production can be performed by a photo-heterotrophic microorganism, such as Chloroflexus aurantiacus. This microorganism is grown autotrophically or photo-heterotrophically to produce 3-HP as an intermediate. Other known microorganisms producing 3-HP from glycerol include Desulfovibrio carbinolicus, D. fructosovorans, Lactobacillus reuteri, Pelobacter venetianus, Ilyobacter polytropus, etc.
However, because of a complicated metabolic pathway, it is difficult to effectively control a process and a decrease in production yield and producibility is expected.
Therefore, there is a desire to produce 3-HP by alternative means.